The main problem concerned the aluminum outer conductor oxide formation and flow, the latter under compression of connector forces. Other types of problems were high radiation of transmitted signal through gaps between the connector assembly and the cable outer conductor, or the introduction of unwanted signal transmitted through the air into the coaxial line. Imperfect seal was also responsible for moisture ingress into the cable which at times lead to low resistance shut between the inner and outer conductors and degradation of the transmitted signal.
Degradation of contact resistance with time in service, as well as ingress of moisture, limited the use of such cable to overhead installations, and in case of sufficient degradation in performance, visual inspections of the cable were made and connectors removed, which permitted removal of collected water, and then the line was re-connected to provide re-establishment of lower contact resistance.
There are many methods by which these mechanical connector problems can be avoided by using metallurgical bonds between the connector and the aluminum outer conductor. All these methods, however, present problems of their own because of high heat and damage to cable insulation, high pressure and damage to coaxial line (alteration of dimensions), high costs, non-portability of equipment, etc.
Fluxless soldering was used and it eliminated additional problems of possible corrosion. A Reynolds Aluminum Company method of fluxless soldering was found to be most suitable. A sleeve with internal diameter dimensions suitable for application over the given coaxial cable was ultrasonically pretinned (solder coated) and with the use of localized heat and pressure was made to solder to both ends of coaxial cables to be spliced. The same principle can be used for cable terminations. The method requires relative movement at the joint interface, and this provides physical disruption of oxides and allows joining to take place.
The shape of the sleeve depends on the method used, or the component configuration used for splicing of the center conductor. It is also a function of how the splices should be matched to the cable. For example, a crimped sleeve over the center conductor has proven reliability but only when applied over solid copper center conductor. The size of the sleeve has to be sturdy enough to have the crimped splice effective. If, however, a coaxial on hand uses a copper-clad aluminum conductor, a crimping method may not give reliable connection because of well-known cold flow of aluminum.
The invention connects the inner conductors of the coaxial cable together by a thin wall sleeve soldered to the conductor ends which are to be connected. By using a thin sleeve, there is no substantial increase in the outside diameter of the inner conductor. The ends of the outer conductor are connected by a sleeve which has opposite end portions that slip over the ends of the outer conductor that are to be connected, and this outer sleeve is somewhat thicker than the inner sleeve so as to provide a strength member which makes the splice as strong, or somewhat stronger, than the coaxial cable beyond the splice.
The inside diameter of the outer sleeve is slightly greater than that of the outer conductor, and it is correlated with the outside diameter of the inner sleeve to match the proportions of the inner and outer conductors from one another along other parts of the cable beyond the splice.
There is ordinarily some increase in the outside diameter of the coaxial cable at the splice; but this change is made without any abrupt shoulder which can catch on the ends of guide surfaces of apparatus used for plowing in the spliced cable. Thus the spliced cable can be plowed in without danger of having splices hang-up in the guides through which the cable has to pass on its way to the plow.
The invention provides a construction in which the coaxial cable can be protected from damage during soldering by heat sinks located in position to hold the parts firmly while soldering, and at the same time carry away heat from the location of the heat application.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.